(a) Field of the Invention
The present invention relates to a polymer for a chemically amplified resist and a resist composition comprising the same. More particularly, the present invention relates to a novel polymer that can be used for a chemically amplified resist composition that can form finer patterns on a substrate in a micro-lithography process suitable for micro-processing of semiconductors, using a mono wavelength as the light source for light exposure, and which improves post exposure delay (PED) stability and has high resistance against the heat produced by dry etching, and a resist composition using the same.
(b) Description of the Related Art
The resist composition is generally used in the preparations of large size integrated circuits (LSI) or in high resolution lithography. Recently, resist compositions with high resolution and high sensitivity have been required due to the densification of large size integrated circuits. Such embodiments of microcircuits in semiconductor integrated circuits generally proceed using a lithography process through which process the microcircuit is constructed by coating resist on a substrate, transcribing patterns on the substrate using a prepared photo mask, and etching the substrate along the transcribed pattern.
Such lithography processes comprise the following steps: (a) a coating step comprising uniformly coating resist on the surface of a substrate, (b) a soft baking step comprising evaporating the solvent from the coated resist film to adhere the resist film to the surface of the substrate, (c) a light exposure step comprising light exposing the substrate while projecting the circuit pattern on the mask, repeatedly and sequentially using a light source such as ultraviolet light to transcribe the pattern of the mask onto the substrate, (d) a development step comprising selectively removing the part in which chemical properties such as solubility change by the exposure to the light source using development liquid, (e) a hard baking step for adhering more firmly the resist film that remains on the substrate after development, (f) an etching step comprising etching the predetermined part along the pattern on the developed substrate in order to impart the electric properties and (g) a stripping step comprising removing the resist that becomes unnecessary after said etching step.
The speed of high-integration of semiconductor integrated circuits has increased 4-fold for 3 years. Thus, at present, in the field of dynamic random access memory (DRAM), 64 mega bit DRAM and 256 mega bit DRAM are mass-produced, and the development of giga bit DRAM has started.
The conventional 16 mega DRAM used the technology of a 0.5 xcexcm circuit line, while 64 mega DRAM uses the technology of a circuit line of 0.3 xcexcm or less, and 256 mega DRAM and giga DRAM requires an ultra micro pattern of less than quarter micro, such as 0.20 xcexcm, 0.18 xcexcm, 0.15 xcexcm depending on the design. In such micro-processing, the light-radiation wavelength moves to deep ultraviolet. Therefore, there is a need for the development of a new resist that can effectively respond to deep ultraviolet light.
The resist of the prior art comprising quinonediazide photoactive material and phenol novolac resin cannot satisfy the above-mentioned requirement, because, in such a resist system, there is a large absorption at the wavelength zone of 300 nm or less and thus, when mono wavelength light-exposure of 300 nm or less is conducted, pattern profile is significantly deteriorated. Therefore, there is a need for the embodiment of a stiff pattern in which the pattern profile does not flow.
In order to embody such a pattern profile, an aligner commonly called a stepper is generally used as a light-exposing apparatus. Such light-exposing apparatuses are divided into an apparatus using G ray (wavelength 436 nm), I ray (wavelength 365 nm) of mercury light, and an apparatus using an excimer laser of mono wavelength KrF (248 nm) and ArF (193 nm) according to the light source. For embodying micro-patterns on the substrate, the resolution value (R) should be small. The resolution value is expressed by the following Rayleigh diffraction limiting equation. Theoretically, since the resolution value becomes smaller as the wavelength of the light source becomes shorter, it is preferable to use a shorter mono wavelength.
[Diffraction limiting equation]
R=xcexaxcex/NA
Wherein, xcexa is a constant, xcex is a wavelength of the light used, and NA is the number of the aperture of the lens.
In order to achieve high resolution of a quarter micron or less, the capacity of degradation of lithography should be improved. For this purpose, it is effective to use a mono wavelength light source having a short wavelength and to increase the aperture number (NA) of the optical lens of the exposing apparatus.
Accordingly, a resist composition that uses a high-output excimer laser light source so as to respond to the high-resolution tendency of semiconductor integrated circuits is commonly used. This composition is for a KrF and an ArF excimer laser, and high-sensitivity resist systems introducing the chemical amplification concept are suggested.
A chemically amplified resist produces acid by photolysis due to the irradiation of ultraviolet light. The produced acid degrades the protective group which is partially protected with the aid of heat, and then it reacts with the acid labile polymer to initiate the chain reaction or act as a catalyst, and thus, one molecule of acid causes a number of bond formation or bond degradation reactions. Therefore, a term xe2x80x9cchemical amplificationxe2x80x9d means the phenomenon whereby active species produced by the action of one photon causes chemical chain reactions to rapidly amplify the yield of quantum. Due to this continuous reaction of acid, the concept of chemical amplification was introduced and used.
A chemically amplified resist is divided into a two-component system comprising an acid-labile polymer and a photo acid producing agent and a three-component system comprising an acid-labile polymer, a photo acid producing agent and a matrix resin. In the resist of the prior art, the degradation or the cross-reaction of a light sensitive material occurs directly at the light exposure part, and, when it is developed, a resist image pattern of a positive or negative form is obtained. However, in the chemically amplified resist, an acid labile polymer or compound is not directly reacted by light exposure, but an acid is produced from the photo acid producing agent in the light-exposed part, and only a latent image is produced. The produced acid acts as a catalyst for the acid labile polymer in the post-exposure bake (PEB) step, and thus, it causes the amplification of the reaction and the significant difference in solubility.
The first resist based upon the chemical amplification concept was a resist using a polyhydroxystyrene derivative poly[p-(t-butyloxycarbonyloxy)styrene] (PBOCSt) blocked with t-BOC (tertiary-butoxy carbonyl) group and onium salt as a photo acid producing agent, and it is described in American Chemical Society, xe2x80x9cPolymers in Electronicsxe2x80x9d, ACS Sym. Series, No. 242, by Ito et al. The reason for using the polyhydroxystyrene derivative is as follows: since the novolac phenol resin that was used in the resist of the prior art largely absorbs deep UV, UV light cannot sufficiently reach the contact surface of the resist substrate. Thus, in the light-exposed part of the resist, chemical changes by light-exposure do not sufficiently occur in the membrane thickness direction, and thus the solubility of the developing liquid becomes irregular. This makes the shape of the section of the resist pattern formed after development triangular. Thus, when the obtained resist pattern is used as an inner etching mask for a substrate, the micro-circuit pattern to be aimed cannot be transcribed. In order to compensate for this, there is a need to change the base polymer, and a polyhydroxystyrene derivative having excellent plasma resistance is known to be suitable.
As examples, a chemically amplified resist comprising poly(p-styreneoxytetrahydropyranol) and an acid producing agent is known by Ueno et al. In the 36th Japanese Applied Physics Society announcement, 1p-k-7, 1989, and a three component system resist comprising novolac phenol resin, bisphenol-A substituted with t-BOC group and pyrogallol methanesulfonic ester is known from Schlegel in the 37th Japanese Applied Physics Society announcement, 28p-ZE4, 1990. In addition, technologies relating to the preparations of said resists are disdosed in JP patent publication Hei. 2-27660, JP patent publication Hei. 5-232706, JP patent publication Hei. 5-249683, and U.S. Pat. Nos. 4,491,628 and 5,310,619. However, while such chemically amplified resists have excellent resolutions compared to the resist for G-ray and I-ray of the prior art, they are likely to be affected by the surrounding environment, particularly by oxygen, moisture and other trace ingredients around the membrane surface, and it is difficult to form stable micro patterns because a trace amount of acid is produced in the light-exposed part.
In addition, MacDonald et al. reported in Proc. SPIE, Vol. 1466. 1991 that trace dimethylanilline contained in the air decreases the activity of the acid produced around the surface of the resist by light exposure, and it produces a layer that hardly melts on the membrane surface, and said hardly-melting layer remains on the surface of the resist pattern after development treatment. However, this process has the problem that footing is caused by the reaction of the micro pattern with the substrate due to the time delay from the light exposure to the PEB process, and a T-top type pattern is produced by environmental pollution due to the amine ingredient distributed in the air in the process line. Therefore, there is a need for compensating the PED stability of the resist composition using said compound, and there is a need for a resist composition using a novel base polymer suitable to embody high sensitivity and high resolution at a wavelength of 300 xcexcm or less.
In addition, recently, large size integrated circuit tends to use a dry etching process. Said dry process is for increasing integration of semiconductor integrated circuit, and changes the manner of etching on the substrate in the lithography process from wet etching having large side etching of the prior art to dry etching having small side etching. In the dry etching process, the resist pattern should not change by the heat produced when etching. In addition, as the degree of integration increases, higher heat resistance is required by the resist used.
Accordingly, it is an object of the present invention to provide a novel polymer that can be applied to a chemically amplified resist composition that can form finer patterns on a substrate in a microlithography process using deep ultraviolet light, improves post exposure delay stability, and has high resistance against the heat produced by dry etching, and a resist composition using the same.
In order to achieve the above object the present invention provides a polymer for a chemically amplified resist represented by the following Formula 1. 
Wherein, R1 is hydrogen or methyl, R2 is hydrogen or CH2CH2COOC(CH3)3, R3 is chloro, bromo, hydroxy, cyano, t-butoxy, CH2NH2, CONH2, CHxe2x95x90NH, CH(OH)NH2 or C(OH)xe2x95x90NH,
xe2x80x83x+y+z=1,x is 0.1-0.9,y is 0.01-0.89,z is 0.01-0.89,
and
n is 1 or 2, and when n is 2, both R2 are the same.
In addition, the present invention provides a resist composition comprising (a) a polymer represented by the formula 1, (b) an acid producing agent and (c) an organic solvent.
The present invention will now be explained in more detail.
In order to synthesize a polymer capable of being alkali developed 10 represented by the formula 1, three monomers constituting a polymer are prepared and they are introduced in a reactor equipped with a reflux cooler under a nitrogen environment and are reacted. Tetrahydrofuran (THF), toluene, benzene, chloroform, carbon tetrachloride, etc. can be used as a polymerization solvent. Azobisisobutyronitrile (AIBN) or benzoperoxide (BPO) can be used as a polymerization initiator. Said polymerization solvent and initiator are added to the reactor and reacted while being stirred. After the reaction completes, the synthesized polymer is precipitated in hexane to obtain precipitates, and then the precipitates rinsed several times and vacuum dried to obtain the polymer.
For synthesizing the monomer having a z repeat unit of the compound of Formula 1, the synthesis of cyanoalkylstyrene by way of Equation 1 should be preceded. To the synthesized 4-cyanoalkylstyrene, t-butyl acrylate and t-butyl methacrylate groups are added, and the prepared monomers are stirred with other monomers such as acetoxystyrene, t-butylacrylate, and t-butyl methacrylate to prepare the polymer.
The process for synthesizing the monomer having a z repeat unit comprises two steps. First, group I cyanide comprising sodium cyanide and s potassium cyanide is mixed with alkyl alcohol comprising water and ethanol, as shown in Equation 1. To said solution, alkyl styrene comprising 4-chloroalkistyrene and halogen atoms is slowly introduced and is reacted to synthesize cyanoalkylstyrene. Then, the monomer obtained in Equation 1 is stirred with t-butylacrylate to synthesize 4-(3cyano-di-1,5t-butoxycarbonyl-pentyl)styrene (CBCPS) as shown in Equation 2. Wherein, cyanoalkylstyrene and triton non-solution or tetraalkylaminehydroxide solution are dissolved in dioxane, and then, t-butylacrylate is introduced and stirred. After the reaction completes, said mixture is neutralized with an acidic solution and is extracted to synthesize CBCPS.
For the synthesis of the polymer of the present invention, THF, toluene, benzene, chloroform or carbon tetrachloride can be used as polymerization solvent. 4-acetoxystyrene or 4-butoxystyrene is added to the prepared CPCBS with 4-butylacrylate or 4-butylmethacrylate, and the polymerization initiator such as AIBN and BPO is added and the mixture is stirred to prepare a polymer. Said polymer has a weight average molecular weight (Mw) of 3,000-30,000, and the degree of dispersion can be controlled from 1.01 to 3.00 depending on the synthetic process.
The substitute monomer used in the present invention exhibits sufficient development inhibiting capacity at the non-light-exposed part, and the substitute group is degraded by the action of acid and is dissolved in developing liquid at the light-exposed part.
The resist composition using the polymer of the present invention comprises (a) a polymer represented by the formula 1, (b) an acid producing agent and (c) an organic solvent.
The resist composition using the polymer of the present invention preferably comprises 1-50 wt % of said polymer.
As the acid producing agent, sulfonium salt, an onium salt such as iodonium, N-iminosulfonate, disulfone, bisarylsulfonyldiazomethane and arylcarbonylarylsulfonyldiazomethane can be used. Preferably, the acid producing agent is contained in the resist composition in an amount of 0.1 to 50 wt %.
The examples of sulfonium salt include the following compounds but are not limited to them. 
The examples of onlum salt include the following compounds. 
The examples of N-iminosulfonates include the following compounds. 
The examples of disulfones include the following compound. 
(Wherein R is H, xe2x80x94CH3 or xe2x80x94(CH3)3.)
The examples of bisarylsulfonyldiazomethanes include the following compound. 
(Wherein R is H, xe2x80x94CH3 or xe2x80x94C(CH3)3.)
The examples of arylcarbonylarylsulfonyidiazomethanes include the following compound. 
(Wherein R is H, xe2x80x94CH3 or xe2x80x94C(CH3)3.)
The organic solvent is preferably selected from the group consisting of ethyleneglycol monoethylether acetate, propyleneglycol monoethylether acetate, ethylether acetate, n-butyl acetate, methyl isobutyl ketone, ethyl lactate, 3-ethoxy-ethylproplonate, 3-methoxy-methylpropionate, diglycol monoethylether, 2-heptanone, diacetone alcohol, xcex2-methoxyisobutyric acid methylester, propyleneglycol monoethylether, propyleneglycol monomethylpropionate, methyl lactate, butyl lactate, ethyl pyruvate, xcex3-butyrol lactone, and a mixture thereof. Preferably, the organic solvent is contained in the resist composition in an amount of 0.1 to 99 wt %.
The resist composition using the polymer of the present invention may comprise a dissolution inhibitor in order to improve the dissolution inhibition of the non-light-exposed part. The use of the dissolution inhibitor makes the difference of solubility of the light-exposed part and non-light-exposed part larger and contributes to the improvement of contrast. Such dissolution inhibiting additives can be added in the resist composition in an amount of 0.1 to 50 wt % based on the weight of the polymer of the present invention.
The examples of the dissolution inhibitor include the following compounds but are not limited to them. 
(Wherein R is a molecule comprising C1-C10 and H and O)
The resist composition using the polymer of the present invention can be applied as follows to obtain a micro-pattern.
When the resist composition using the polymer of the present invention is formed as a thin layer on a substrate such as a silicone wafer and is treated with a base aqueous solution, the dissolution does not occur because the solubility of the copolymer is low. However, when deep ultraviolet light is radiated, the resist responds and the add producing agent in the resist produces acid, and the development inhibiting substituent causes the degradation of the polymer structure by the action of heat addition in the light-exposed part and the acid is produced again. Consequently, one acid that was produced causes chemical amplification which causes a plurality of acid active degradation. As a result, the solubility of the polymer largely increases in the light-exposed part, and, when developing with the base aqueous solution, the difference in the solubilities of the light exposed part and non-exposed part appears. Thus, a resist composition having excellent resolution compared to the resist composition using G-rays and I-rays of the prior art can be obtained.
The present invention will be explained in more detail with reference to the following Examples and Comparative Examples. However, these are to illustrate the present invention, and the present invention is not limited to them.
The Synthesis of 4-Cyanomethylstyrene(CyMS)
In a 500 xcexcl 4-opening flask equipped with a stirring bar, 49.01 g of sodium cyanide was mixed with 70.07 g of water and 50.96 g of ethanol. Then, the temperature of the flask was elevated to 60xc2x0 C. and the sodium cyanide was completely dissolved. To said solution; 87.50 g of 4-chloromethylstyrene was slowly added and it was reacted for 3 hours while stirring and maintaining the reaction temperature within 60-70xc2x0 C. When the reaction terminated, said solution was cooled to 40xc2x0 C., and 100 g of diethylether was added and the diethylether layer was separated. The separated organic layer was extracted with 300 g of water three times, and the water layer was extracted with 50 g of diethylether and was combined with said organic layer. The separated obtained organic layer was dried with magnesium sulfate for one day, and then the organic solvent was removed using an evaporator to obtain the product 4-cyanomethylstyrene. The yield of the product was 80%, and the product was a deep purple color.
Said synthesis was according to the Equation 1. 
The Synthesis of 4(3-Cyano-di-1,5-t-butoxycarbonyl-pentyl)styrene (CBCPS)
In a 500 ml 4-opening flask equipped with a stirring bar, 57.28 g of 4-cyanomethylstyrene prepared in the above process and 1.4 g of triton non solution were dissolved in 40 g of dioxane. 102.54 g of t-butylacrylate were slowly added to said solution for 30 minutes while maintaining the temperature of the reactor at 60xc2x0 C., and it was reacted for 24 hours while stirring. After the reaction, the reactant was neutralized with a chloride solution, and the neutralized reactant was extracted with 100 g of diethylether and 300 g of water three times, the water layer was extracted with 50 g of diethylether and combined with the organic layer. The separated obtained organic layer was dried with magnesium sulfate for one day, and then the organic solvent was removed using an evaporator. The obtained product was distillated under reduced pressure to remove unreacted material, and it was recrystallized with methanol to obtain light yellow CBCPS in a 60% yield.
Said synthesis was according to the Equation 2. 
The synthesis of the polymer of Formula 1
In a 500 ml 4-opening flask equipped with a temperature controlling apparatus and a nitrogen introducing apparatus, 300 ml of THF were introduced and nitrogen was purged and it was stirred for 30 minutes. To said reactor, 56.62 g of 4-acetoxystyrene, 9.16 g of t-butylacrylate and 24.14 g of CBCPS prepared in the above process were added, 1.21 g of AIBN was added and stirred for 30 minutes under a nitrogen atmosphere while maintaining the temperature at 40xc2x0 C., and the temperature of the reactor was then elevated and the reactant was stirred for 24 hours while refluxing. After the completion of the reaction, the temperature was lowered to room temperature and the reactant was deposited in 3 liters of hexane to obtain the precipitates. The obtained precipitates were filtered and rinsed with 2 liters of hexane several times and were vacuum dried. The dried macromolecule was dissolved in 300 ml of methanol in a flask, and 50 ml of 30% NH4OH aqueous solution were added and the mixture was slowly stirred, and, after the polymer was completely dissolved, the mixture was additionally stirred for 30 minutes. The solution was deposited in 1.5 liters of water to obtain the precipitates, and the precipitate were filtered and rinsed with 2 liters of pure water and vacuum dried to obtain 58.23 g of polymer of Formula 1.
The above synthesis was according to Equation 3. 